What is a tempo run? Simply put, a tempo run is like an Oreo cookie—with the cookie part the warmup and cool-down (easy-paced running) and the filling (good stuff) running at a comfortably hard effort for a sustained period of time.

What is the purpose of a tempo run? The goal is to run at a sustained effort to raise your red line, the pace at which you switch from burning mostly fat to precious stores of glycogen. This red line is also referred to as the anaerobic threshold. When you raise your red line, you are able to run faster while using fat as a primary fuel source (you could run for days on fat) while preserving glycogen stores. Some runners also use a tempo workout to run at a consistent pace to learn how to run at a specific pace (race pace, for example).

A traditional tempo workout includes a 10 to 15 minute warmup, 20 to 30 minutes at tempo effort, and a 10 to 15 minute cool-down. There are a variety of tempo workouts, some longer and some shorter, but they all focus on running around your red line.

How do you know where your red line is? Gone are the days of estimating your tempo pace by a past race time, personal record, estimated finish time, height, weight, number of Facebook friends...That, my friends, is a little like predicting next month's weather. Think about it—what does a race performance in the future have to do with the status of your red line now? A race you did three months ago in 50 degree weather has little to do with running a tempo in 80 degree heat. Read my lips: It is not about pace. It's about your body, your effort level and the moment. Pace is the outcome of the tempo workout, not the target.

Your tempo pace at the beginning of the season will likely be slower than at the end due to fitness improvements. It will also vary in weather elements, fatigue levels, cycle status, and more. For instance, a tempo workout done heading into a 10 to 15 mph headwind will be different pace-wise than one with no wind or a tailwind. The goal is to find your red line and hold it there. That takes practice, patience, and mindfulness.

How do you find your red line? This is so easy it will make you smile. Although it may seem like finding a needle in a haystack, it will become quite clear where your red line is with some practice. One way to find it is to plan a run on predictably flat terrain and then...

Warm up walking easy three minutes and begin to tune into your breath and watching your pace.

Pick up the walking pace for two more minutes, again tuning into your breath.

Recite the words to the Pledge of Allegiance out loud paying close attention to your breath and how easily you are able to speak the words.

Increase the speed to a very easy run (very easy) for two minutes and recite the Pledge again at the end of this set.

If you can recite it easily—continue to progress the speed very gradually and repeat for two minutes at that speed reciting the Pledge of Allegiance at the end of each set.

When you reach the point at which you can no longer say the words out loud easily—you are at, near, or close to your red line. This is also the point many describe as comfortably hard and an effort where you can hear your breathing but you're not gasping for air.

Once found, make note of your pace, heart rate, and, most importantly, how it feels.

The key is in understanding what it feels like and learning to run at that effort rather than a pace. When you do that, you will run a perfect tempo workout every time, because you are self-regulating for every condition (heat, wind, stress, fatigue, improved fitness, et cetera). If you continue to train by one pace, you become good at running at that pace, but you're not necessarily training to raise your red line. Make sense? The bonus is, it teaches you how to pace yourself without a watch and make the most of every workout.

Run at an easy effort for 10-15 minutes to continue to warm up. This should be at an effort where you can talk easily (or recite the Pledge).

Run twenty minutes at tempo effort—at a point at which you can no longer talk easily but you're not gasping for air. Hold it there and be mindful of your pace and other variables on the day.

If you are new to this and overwhelmed by the thought of running at this effort level for a full 20 minutes, break it into shorter segments and add 1-2 minutes of walking in between. For instance, running 10 minutes twice with 2-3 minutes in between or for four times at 5 minutes with 1-2 walking or easy jogging minutes in between.

Finish with 10 minutes of easy running and a 3-minute walking cool-down and you're done!

Keep track of the variables (weather, fatigue, energy, stress, date) as well as your pace and how you felt. Running at the right effort will not only allow you to improve faster, you'll be motivated to train consistently!

This DIY Threshold Assessment is a modified version from the book Be a Better Runner by Sally Edwards and Carl Foster. If you're more scientifically inclined, you can track your heart rate along with pace or schedule a VO2 Max test where they'll find it for you.

New devices are coming out all the time that help you to find your training zones versus relying on inaccurate formulas and calculations. One that I'm working with currently is PEAR Sports, where a coach (like me, or Matt Fitzgerald) guides you via audio to find your zones and through a variety of running workouts. It tracks heart rate, cadence, and more, and we guide you in knowing when you're in or out of zone based on your body in the moment.

[Disclosure: I am affiliated with and a professional coach with PEAR Sports.]